1. Field of the Invention
This invention relates to limited-slip differentials for wheeled vehicles, particularly relates to a type of fluctuating gear-ratio limited-slip differential.
2. Background of Related Art
Limited-slip differentials are well known and take different forms; the working principle can be divided into inner friction model, overrunning model, electronic controlled automatic differential locker, the limited slip function realized using ABS brake system, and potential barrier model. Each model has some defects.
For inner friction model, which is the most widely used model of limited slip differentials, can be subdivided into preloaded and non-preloaded, both have the defects of higher price, and the later may be even more expansive, while the former may leads to a higher steering resistance and increased tire wear.
The overrunning model has complicated structure, works roughly, and some types have a lower reliability.
The electronic automatic differential locker also works roughly, being complicated in structure.
The limited-slip function realized by ABS system consumes more power.
This patent reveals a type of limited-slip differential belonging to potential barrier model, having the advantage of simple structure, higher reliability and true traction. The function is realized by periodic change in gear ratio between the pinions and the side gears, and the pinions have an odd number of the gear ratio fluctuating period in one revolution, so that when the gear ratio between the pinions and one side gear reaches the maximum, the gear ratio between the pinions and the other side gear gets the minimum, thus an unequal distribution of the torque on two side gears is realized. If the pinions rotate an angle of a half period of the speed ratio fluctuation, the torque distribution on both side gears is interchanged. The periodic change in the torque bias ratio forms two potential barriers, if the ratio of the torque acted on side gears does not reach the maximum torque bias ratio, the differential cannot make a continuous differential rotation, thus the slip of the driving wheel is limited. But up to now for available product, the period of the speed ratio fluctuation is only one pitch. In each pitch the pinions and the side gears will undergo a process of relative angular acceleration and deceleration, the relative angular acceleration is rather higher, the value is proportional to the changing range in gear ratio, and proportional to the square of the number of speed ratio periods involved in one revolution of the pinions. A larger relative angular acceleration will lead to higher relative curvature between tooth surfaces and lower load capacity, tends to make noise. Although the fluctuating range in gear ratio can be improved to a certain extent by means of optimization, the effect is limited. A further increment in the range of gear ratio will lead to a rapid increment in relative curvature between tooth surfaces, or even generate an edge on tooth surfaces. According to traditional design method of one-pitch period, the maximum speed ratio resulted in differential movement between two side gears is only 1:1.38 for a gear pair of 7 teeth in a pinion and 12 teeth in a side gear; and the speed ratio is reduced to 1:1.31 for a gear pair of 9 teeth in pinion and 12 teeth in side gears, it is not sufficient for the requirement of off-road vehicles.